Hydrogels represent a desirable class of materials for many biomedical applications, including the formation of contact lenses. Hydrogels are hydrated, cross-linked polymeric system that contain water in an equilibrium state. Silicone hydrogels are a well known class of hydrogel and are characterized by the inclusion of silicone. Silicone hydrogels generally have a water content greater than about 5 weight percent and more commonly between about 10 to about 80 weight percent. Such materials are usually prepared by polymerizing a mixture containing at least one silicone-containing monomer and at least one hydrophilic monomer. Either the silicone-containing monomer or the hydrophilic monomer may function as a crosslinking agent (a crosslinker being defined as a monomer having multiple polymerizable functionalities) or a separate crosslinker may be employed. Applicable silicone-containing monomeric units for use in the formation of silicone hydrogels are well known in the art and numerous examples are provided in U.S. Pat. Nos. 4,136,250; 4,153,641; 4,740,533; 5,034,461; 5,070,215; 5,260,000; 5,310,779; and 5,358,995. Specific examples of applicable silicone-containing monomeric units include:
(a) bulky polysiloxanylalkyl (meth)acrylic monomers, commonly referred to as "TRIS" monomers, including for example: methacryloxypropyl tris(trimethylsiloxy)silane; PA1 (b) poly(organosiloxane) monomeric units; PA1 (c) silicone containing monomers includes silicone-containing vinyl carbonate or vinyl carbamate monomers such as; 1,3-bis4-vinyloxycarbonyloxy)but-1-yl!tetramethyldisiloxane; 3-(trimethylsilyl)propyl vinyl carbonate; 3-(vinyloxycarbonylthio)propyltris(trimethylsiloxy)silane!; 3-tris(trimethylsiloxy)silyl! propyl vinyl carbamate; 3-tris(trimethylsiloxy)silyl! propyl allyl carbamate; 3-tris(trimethylsiloxy)silyl!propyl vinyl carbonate; t-butyldimethylsiloxyethyl vinyl carbonate; trimethylsilylethyl vinyl carbonate; trimethylsilylmethyl vinyl carbonate. Other examples of applicable silicone-containing monomers are well known in the art. PA1 R and D independently are alkyl, alkylene or haloalkyl groups having 1 to 10 carbon atoms wherein said carbon atoms may include ether linkages therebetween; PA1 R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from: alkyl or haloalkyl groups wherein ether linkages may be included between carbon atoms; siloxane groups; and carbocyclic ring groups having from 6 to 18 carbon atoms; PA1 m is an integer from 1 to 500; n is an integer from 1 to 20; x and y are 0 or 1; PA1 z is 1 or 2;and x+y+z=3; PA1 so long as at least one of R.sub.1 or R.sub.2 is an alkyl group having from 1 to 10 carbon atoms. PA1 R and D independently are an alkyl, alkylene or haloalkyl group having 1 to 10 carbon atoms wherein said carbon atoms may include ether linkages therebetween; PA1 R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from: alkyl or haloalkyl groups, (including both unsubstituted alkyl groups e.g. groups having from 1 to 18 carbon atoms, and substituted alkyl groups e.g. halogen substituted alkyl and hydroxy substituted alkyl), wherein ether linkages may be included between carbon atoms; siloxane groups; and carbocyclic ring groups having from 6 to 18 carbon atoms, e.g. cyclohexyl or phenyl groups which may include alkyl side groups; PA1 m is an integer equal to 1 or greater but is preferably less than 500, and more preferably from 1 to about 10, and still more preferably from 1 to 3; PA1 n is an integer from 1 to 20 but is preferably from 1 to 6; PA1 x and y are 0 or 1; PA1 z is 1 or 2;and x+y+z=3; PA1 R' and R" independently are an alkyl or alkylene group having 1 to 10 carbon atoms wherein the carbon atoms may include ether linkages therebetween; PA1 R.sub.8 through R.sub.17 are independently selected from monovalent hydrocarbon radicals or halogen substituted monovalent hydrocarbon radicals having 1 to 18 carbon atoms which may include ether linkages therebetween, but preferably are chosen from the groups described with reference to R.sub.1 though R.sub.4 ; PA1 a is an integer equal to or greater than 1; PA1 b and c are integers equal to or greater than 0; and PA1 a+b+c equals an integer from 1 to 1000. PA1 D' is an alkyl or alkylene group having 1 to 10 carbon atoms wherein said carbon atoms may include ether linkages therebetween; PA1 M' is hydrogen, fluorine, or alkyl group (e.g. an alkyl group having from 1 to 10 carbon atoms) but preferably hydrogen or fluorine; and PA1 s is an integer from 1 to 20, preferably 1 to 6. PA1 d+e equals an integer from 2 to 1000, preferably 2 to 100, PA1 f+g equals an integer from 2 to 1000, preferably 2 to 100, PA1 wherein e and g are preferably integers from about 20 to about 50, and PA1 h is an integer from 1 to about 20. PA1 each R.sub.18 independently denotes hydrogen or methyl; PA1 each R.sub.19 independently denotes a lower alkyl radical or a phenyl radical; and PA1 h is 1 to 10. PA1 R.sup.Si denotes a silicone-containing organic radical; PA1 R.sub.20 denotes hydrogen or methyl; PA1 d is 1, 2, 3 or 4; and PA1 q is 0 or 1. PA1 e is 1 to 200; PA1 n' is 1, 2, 3 or 4; and PA1 m' is 0, 1, 2, 3, 4 or 5. PA1 D denotes an alkyl diradical, an alkyl cycloalkyl diradical, a cycloalkyl diradical, an aryl diradical or an alkylaryl diradical having 6 to 30 carbon atoms; PA1 G denotes an alkyl diradical, a cycloalkyl diradical, an alkyl cycloalkyl diradical, an aryl diradical or an alkylaryl diradical having 1 to 40 carbon atoms and which may contain ether, thio or amine linkages in the main chain; PA1 * denotes a urethane or ureido linkage; PA1 a is at least 1; PA1 m' is at least 1; and PA1 p is a number which provides a moiety weight of 400 to 10,000; PA1 each of E and E' independently denotes a polymerizable unsaturated organic radical represented by Formula XII: ##STR15## wherein: R.sub.23 is hydrogen or methyl; PA1 R.sub.24 is hydrogen, an alkyl radical having 1 to 6 carbon atoms, or a --CO--Y--R.sub.26 radical PA1 R.sub.25 is a divalent alkylene radical having 1 to 10 carbon atoms; PA1 R.sub.26 is a alkyl radical having 1 to 12 carbon atoms; PA1 X denotes --CO-- or --OCO--; PA1 Z denotes --O-- or --NH--; PA1 Ar denotes an aromatic radical having 6 to 30 carbon atoms; PA1 w is 0 to 6; PA1 x is 0or 1; PA1 y is 0 or 1; and PA1 z is 0 or 1. PA1 E is hydrogen or methyl, PA1 G is (CH.sub.2)rC(O)OSi(V).sub.3 or hydrogen, PA1 V is methyl, ethyl or propyl, PA1 q is an integer form 1 to 15, PA1 r is an integer form 1 to 10, PA1 q+r is an integer form 1 to 15, hereinafter referred to as NATA. PA1 R.sub.30 and R.sub.31 are independently selected from methyl of cyclohexyl radicals.
Silicone-containing monomers may be copolymerized with a wide variety of hydrophilic monomers to produce a variety of silicone hydrogel products. For example, silicone hydrogels are particularly useful in a variety of biomedical applications including the formation of shaped articles and coatings such as; membranes, films, artificial ureters, diaphragms, intrauterine devices, heart valves, vessel substitutes, surgical devices, catheters, mouth guards, denture liners, intraocular devices, prosthetic devices, and especially contact lenses.
Suitable hydrophilic monomers for use in silicone hydrogels include: unsaturated carboxylic acids, such as methacrylic and acrylic acids; acrylic substituted alcohols, such as 2-hydroxyethylmethacrylate and 2-hydroxyethylacrylate; vinyl lactams, such as N-vinyl pyrrolidone; and acrylamides, such as methacrylamide and N,N-dimethylacrylamide. Still further examples are the hydrophilic vinyl carbonate or vinyl carbamate monomers disclosed in U.S. Pat. No. 5,070,215, and the hydrophilic oxazolone monomers disclosed in U.S. Pat. No. 4,910,277. Other suitable hydrophilic monomers will be apparent to one skilled in the art.
In particular regard to contact lenses, the fluorination of certain monomers used in the formation of silicone hydrogels has been indicated to reduce the accumulation of deposits on contact lenses made therefrom, as described in U.S. Pat. Nos. 4,954,587, 5,079,319 and 5,010,141. Moreover, the use of silicone-containing monomers having certain fluorinated side groups, i.e. --(CF.sub.2)--H, have been found to improve compatibility between the hydrophilic and silicone-containing monomeric units, as described in U.S. Pat. Nos. 5,387,662 and 5,321,108.
Many silicone hydrogels possess relatively high moduli (Young's modulus of elasticity), e.g. often in excess of 300 g/mm.sup.2 as measured by ASTM test method D1938. For many biomedical applications, it is desirable to provide hydrogels having reduced moduli, e.g. in the range of about 20 g/mm.sup.2 to about 150 g/mm.sup.2, and more preferably from about 30 g/mm.sup.2 to about 100 g/mm.sup.2. This is particularly important in the formation of soft contact lenses, as the modulus of lens material can have a significant impact upon lens "comfort." Lenses possessing high moduli often have a perceived stiffness and undesirably high elastic recovery resulting in an unnatural feeling when worn upon the eye.
The use of bulky polysiloxanylalkyl methacrylates, e.g. methacryloxypropyl tris (trimethylsiloxy) silane, referred to above as "TRIS", are known to reduce the modulus of one class of silicone hydrogels, i.e. polyurethane-polysiloxane hydrogel compositions. See for example; Lai, Yu Chin, The Role of Bulky Polysiloxanylalkyl Methacrylates in Polyurethane-polysiloxane Hydrogels, Proceedings of the American Chemical Society Division of Polymeric Materials: Science and Engineering, Vol 72, pg. 118-119, (1995). The use of TRIS compounds in silicone hydrogels is also described in U.S. Pat. No. 5,358,995. In U.S. Pat. Nos. 5,321,108 and 5,387,662, a TRIS-type compound is disclosed which includes at least one fluoro substituted end group including a terminal hydrogen. Such materials are described as providing increase compatibility as between silicone-containing and hydrophilic monomeric units.
Unfortunately, the aforementioned TRIS-type fluorinated compounds have relatively high boiling points, and as such, are not distillable through conventional techniques. As a consequence, purification of such materials can be difficult. For this same reason, these materials can also be difficult to analyze, e.g. by way of gas chromatography.
Thus, silicone hydrogels are sought which maintain acceptable oxygen permeability while possessing reduced moduli and which are more easily synthesized, purified, and analyzed. Furthermore, in many applications, such hydrogels must be optically clear, manufacturable (e.g., capable of being molded, machined, etc.) into such products as contact lenses, biocompatible, and less prone to deposit formation.